The present invention pertains to an apparatus for counterbalancing unsymmetrically distributed centrifugal forces in a rotating body, and, in particular, to a balancing apparatus for counterbalancing an unbalanced batch of laundry being rotated at high speeds within a laundry machine for purposes of water extraction.
In contemporary laundry appliances, such as automatic washing machines and dryers, wherein clothes are washed and centrifuged in the washer and then transferred to the dryer for clothes drying, or in combination washer-dryers wherein clothes are washed, rinsed, spun dry and tumbled dry with the application of heat energy, the drying time required to dry the clothes is dependent on several factors, including the applied heat and the amount of moisture retained in the clothes at the commencement of the drying cycle. When washers are used without a complementary dryer and the washed clothes are line dried, the amount of moisture similarly impacts drying time. Thus, in order to reduce the drying time, the excess moisture of the clothes is desirably reduced before the drying cycle.
One technique frequently employed to extract water from the clothes is to provide a high rotating drum speed during the extraction part of the wash cycle to remove large amounts of water from the load prior to its tumble or line drying. One problem with such a spinning technique is that when a load or batch of clothes is introduced into the clothes basket or cylinder, the load is frequently distributed in such a manner that the center of mass of the loaded cylinder will not coincide with the cylinder axis, thereby producing an unbalanced centrifugal force which is directly proportional to the mass of the unbalanced portion of the total rotating mass, the square of the angular velocity of such unbalanced mass and the radius of the unbalanced mass from the axis of rotation of the cylinder.
Besides affecting the power input required to rotate the cylinder, an unbalanced condition may cause serious vibrations during cylinder rotation. The vibrations may be sufficiently great to actually cause the laundry machine to lift from its support and produce a violent movement of the machine which is colloquially referred to as "walking".
To overcome these vibrational problems, previous laundry machines have employed a variety of tactics. For instance, some laundry machines operate at a sufficiently limited spin speed such that the unbalanced loads typically encountered during operation are insufficient to produce a sufficient amount of centrifugal force to lift the machine form its support and produce "walking" of the machine. Other machines reduce spin speeds upon sensing a severe vibration occurrence. While useful to some extent, these devices have the disadvantage of slowing the overall drying process as the rate at which water is extracted during the period of time in which they are operating is less than desired. Extra moisture retained in the clothes is therefore required to be removed either by a longer period of line drying or by additional consumption of heat energy in machine drying as a longer drying period is necessitated.
Other balancing mechanisms have suspended the entire laundry mechanism on a pivot along with an additional mass producing, dead weight within the enclosing cabinet on a complex spring system. The suspended system is permitted to vibrate within the cabinet in which it is enclosed, and the dead weight tends to reduce undesirable effects of the unbalanced centrifugal forces. A shortcoming of these designs is that, to accommodate the vibratory motion, the size of the clothes basket must be smaller for a given size cabinet, thereby reducing washer capacity.
Another technique for overcoming vibration tendencies of an eccentric loading within a rotating clothes basket is to selectively fill tanks provided around the periphery of the clothes basket with fluid to counterbalance the eccentric mass during certain portions of the rotation of the clothes basket. An assortment of devices intended to realize this technique are known, and representative devices are disclosed in U.S. Pat. Nos. 2,886,979, 3,119,773, 3,135,688, 3,190,447, 3,306,453 and 3,983,035. While perhaps having some utility to overcome vibrational problems, these devices are not without their shortcomings.
For example, while many prior art washers with balancing pockets perform balancing of the unbalanced load after a critical speed of the washer has been reached, for rotational speeds above a one gravity (one G) producing speed and below the critical speed, no balancing is performed. However, significant vibrations, especially with heavy loads such as blankets or pillows, are likely to occur at below critical speed. Consequently, the designers of these washers typically resorted to providing bulky dampening devices and an appreciable space between the wash tub and cabinet to allow for the vibrational movements or oscillations of the clothes basket and tub assembly caused by unsymmetrical centrifugal forces produced at below critical speed. These spaces undesirably increased the size of the washing machine or necessitated a smaller capacity clothes basket be used.
Another shortcoming of the prior art is that the components used to selectively introduce water into the appropriate balancing pockets are frequently complicated in design and assembly. As a result, installation and maintenance of the balancing apparatus may be time consuming and expensive.
Thus, it is desirable to provide a balancing system for a rotating apparatus which overcomes these and other shortcomings of the prior art.